Jay Pipes <jaypipes@gmail.com> 于2019年1月2日周三 下午10:48写道：
On 12/21/2018 03:45 AM, Rui Zang wrote:
It was advised in today's nova team meeting to bring this up by email.
There has been some discussion on the how to track persistent memory resource in placement on the spec review [1].
Background: persistent memory (PMEM) needs to be partitioned to namespaces to be consumed by VMs. Due to fragmentation issues, the spec proposed to use fixed sized PMEM namespaces.
The spec proposed to use fixed sized namespaces that is controllable by the deployer, not fixed-size-for-everyone :) Just want to make sure we're being clear here.
The spec proposed way to represent PMEM namespaces is to use one Resource Provider (RP) for one PMEM namespace. An new standard Resource Class (RC) -- 'VPMEM_GB` is introduced to classify PMEM namspace RPs. For each PMEM namespace RP, the values for 'max_unit', 'min_unit', 'total' and 'step_size` are all set to the size of the PMEM namespace. In this way, it is guaranteed each RP will be consumed as a whole at one time.
An alternative was brought out in the review. Different Custom Resource Classes ( CUSTOM_PMEM_XXXGB) can be used to designate PMEM namespaces of different sizes. The size of the PMEM namespace is encoded in the name of the custom Resource Class. And multiple PMEM namespaces of the same size (say 128G) can be represented by one RP of the same
Not represented by "one RP of the same CUSTOM_PMEM_128G". There would be only one resource provider: the compute node itself. It would have an inventory of, say, 8 CUSTOM_PMEM_128G resources.
CUSTOM_PMEM_128G. In this way, the RP could have 'max_unit' and 'total' as the total number of the PMEM namespaces of the certain size. And the values of 'min_unit' and 'step_size' could set to 1.
No, the max_unit, min_unit, step_size and total would refer to the number of *PMEM namespaces*, not the amount of GB of memory represented by those namespaces.
Therefore, min_unit and step_size would be 1, max_unit would be the total number of *namespaces* that could simultaneously be attached to a single consumer (VM), and total would be 8 in our example where the compute node had 8 of these pre-defined 128G PMEM namespaces.
We believe both way could work. We would like to have a community consensus on which way to use. Email replies and review comments to the spec [1] are both welcomed.
Custom resource classes were invented for precisely this kind of use case. The resource being represented is a namespace. The resource is not "a Gibibyte of persistent memory".
The point of the initial design is avoid to encode the `size` in the resource class name. If that is ok for you(I remember people hate to encode size and number into the trait name), then we will update the design. Probably based on the namespace configuration, nova will be responsible for create those custom RC first. Sounds works.
Best, -jay
Regards, Zang, Rui